This invention relates to a new mechanical face seal design which improves the performance characteristics of the seal. A mechanical face seal is a device which controls fluid leakage between two regions under different pressures while allowing a rotating shaft to pass between the regions. Such seals are widely used in ships, submarines, process pumps, and compressors.
Conventional mechanical face seals will often leak and sometimes have short lives because the geometry between the seal faces deviates from parallel due to various thermal- and pressure-caused distortions of the seal. Mechanical seals are generally known as troublesome devices because it is most often the failure of a seal which necessitates the rebuilding of a pump. Mechanical seals, in general, have only a fraction of the life of bearings. Seals having longer life with low leakage and reliable performance would serve to upgrade the performance of mechanical equipment and reduce the cost of operation. Conventional seals usually have high thermal distortion, and they are so rigid (low radial compliance) that the faces cannot deflect back to the desired parallel condition.
Attempts have been made in the prior art to achieve radial compliance, but these attempts have not been entirely successful. U.S. Pat. No. 4,212,475, entitled SELF ALIGNING SPIRAL GROOVE FACE, to Sedy; Sedy, Josef, "Improved Performance of Film-Riding Gas Seals Through Enhancement of Hydrodynamic Effects," ASLE Preprint No. 78-LC-3B-1, October, 1978; and Sedy, Josef, "A New Self-Aligning Mechanism for the Spiral-Groove Gas Seal Stability " ASLE Preprint No. 79-LC-3B-3, October, 1979; all disclose the use of a low Young's modulus material ring to enhance compliance with an opposing ring. However, the Sedy seal does not completely remain parallel; some degree of angular misalignment remains. This misalignment is probably due to the long length or thickness of the Sedy ring which thus has a high stiffness.
Other prior art seals have not been successful in achieving radial compliance and alignment. U.S. Pat. No. 3,921,986, entitled SHAFT SEAL, to Geary et al., discloses the use of a resilient mounting to aid in ring alignment; however, this patent does not disclose the use of a compliant or conformable ring to assist in the alignment. U.S. Pat. No. 4,099,728, entitled MECHANICAL SEAL ASSEMBLY, to Wiese, discloses a seal having a soft material nonrotatable sealing ring and a hard material backup ring; however, the seal design is rigid, and thus misalignment occurs. U.S. Pat. No. 4,991,450, entitled SHAFT SEAL RESISTANT TO ELECTROKINETIC CORROSION, to Beck, discloses a seal having a hard element attached to one ring and a soft element attached to another ring; however this patent does not disclose the use of the varying hardness materials for the rings, themselves.
Accordingly, it is a primary object of the present invention to provide a seal having minimal or no leakage, a high tolerance to variable operating conditions, a long life, and high duty capabilities.
It is another object of the present invention to provide a radially compliant seal ring and a zero net thermal rotation seal design.
Yet another object of the present invention is to provide a seal which enhances radial compliance and zero net thermal radial taper.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description to follow, taken in conjunction with the accompanying drawing.